A major consideration in planning wireless units is reducing their power utilization so that they may be used for as long a period as possible after recharging. In wireless networks, when a wireless unit is not in use it moves into a sleep state having a low power consumption level. The wireless unit moves back to a normal state when it receives a transmission. In packet based networks, various network managing tasks are performed by transmitting control packets to all the nodes of the network. As wireless packet based networks are planned to be an integral part of a packet based network, the wireless units in the network also receive the control packets. The reception of the control packets by the wireless units, wakes the wireless units and uses their battery power.
For example, address resolution protocol (ARP) packets are transmitted by a sender unit to all the nodes of the network in order to determine the address of a destination to which the sender is interested in transmitting data.
The request for comments RFC 3220, the disclosure of which is incorporated herein by reference, describes an ARP proxy that services end units, intercepts ARP packets and responds to the ARP packets, if necessary, instead of the end units. Similar provisions are described in “ProxyARP Subnetting HOWTO”, by Bob Edwards and in “Proxy ARP with Linux”, by David Weis, the disclosures of which documents are incorporated herein by reference.
A dynamic host configuration protocol (DHCP) is used to configure IP units in a packet based network. Among other tasks, DHCP is used to automatically assign IP addresses to units. Generally, in a simplified manner, when a unit needs an IP address so that it can be contacted, the unit transmits a DHCP request with a broadcast address. An address server in charge of allocating the IP addresses generates a DHCP response packet with the requested IP address and transmits the response packet to the requesting unit, with a broadcast or unicast address. DHCP response packets with broadcast addresses are commonly used for the last step of the transmission, so that the response packets reach their destination even if the destination is not in the same local network (e.g., VLAN) as the sender, and a router along the path needs to provide the destination address of the requesting unit.
DHCP requests are for allocation of addresses, and for other tasks which should be performed by a single entity or by a plurality of coordinated entities. ARP requests are requests for address information which may be supplied by any unit knowing the information.
U.S. Pat. No. 5,920,699 to Bare, the disclosure of which is incorporated herein by reference, describes a switch that directs DHCP requests through a port leading to the address server according to the IP address of the address server in the DHCP request packet, if the IP address appears in the packet and the switch previously learned the port leading to the target location. According to the U.S. Pat. No. 5,920,699, if either the port leading to the address server is not known or the DHCP packet does not contain a specific server IP address, then the switch broadcasts the packet out all its ports.
For broadcast DHCP replies, the U.S. Pat. No. 5,920,699 suggests keeping track of the transaction ID in the DHCP requests handled by the switch and using the tracked IDs to direct broadcast DHCP replies back through the port leading to the requesting unit.
The method of the U.S. Pat. No. 5,920,699 is not sufficient in cases in which many wireless units are located behind a single port, as is commonly performed. In addition, the method of the U.S. Pat. No. 5,920,699 is relatively complex as it requires keeping the state of DHCP requests in order to correlate between the requests and replies.